Pressure sensing device



Nov. 4, 1969 F. F. FREEMAN 3,476,399

PRESSURE SENSING DEVICE Filed Oct. 20, 1965 I0 4 2 l V Z l7 aj L l 15 3 Id 9 LVVENTOR.

FORREST F. FREEMAN United States Patent 3,476,899 PRESSURE SENSING DEVICE Forrest F. Freeman, Potter Valley, Calif. (7205 NE. 43rd Ave., Vancouver, Wash. 98661) Filed Oct. 20, 1965, Ser. No. 498,454 Int. Cl. H0111 35/18 U.S. Cl. 20084 6 Claims ABSTRACT OF THE DISCLOSURE A fluid pressure operated switch responsive to diflerential pressures. Operation of the switch is dependent on applying fluid pressure on opposed faces of a carton piston through the end walls of an electrically conductive housing. The piston is guided for movement, due to variations in pressure, by the inner wall surface of said housing and closes a circuit when the piston engages a pointed contact extending into said housing through One of its end walls.

This invention relates to a fluid pressure sensing device capable of responding to slight variations in differential pressures and more particularly to a fluid pressure sensing device whose operation is dependent of the diflerence in pressure existing on opposed faces of a light weight movable carbon piston.

In many instances it is desirable to have a fluid pressure sensing device to give an indication when the desired pressures are being sustained such as the pressures in plenum chambers and air distribution systems, and also in positive or closed crane cask ventilation systems now being used on internal combustion engines to help reduce emmission of smog, or any application where there is differential pressures. The present invention provides an extremely simple fluid pressure sensing device that may be operated by a very slight movement of gases and yet is inexpensive to manufacture, easy to install, and is trouble free and virtually foolproof.

The invention will be further described with reference to the attached drawing which is an example of the pressure sensing device.

Referring to the drawing in detail there is shown a pressure sensing device having a metal housing 1 provided with an inner bore 7 which may be of any crosssectional shape, for example, cylindrical and having end wall 3 and end cap 4 closing the ends of bore 2, a float or piston 5 is disposed within the bore 2 and is preferably formed of a light weight electrical conductive material, such as, a carbon composition. Float 5 is in slidable relation to the wall of bore 2, and has substantially the same cross-sectional shape as the bore 2 to allow movement of the float 5 within the bore 2. The peripheral edge of float 5 cooperating with the wall of bore 2 provides electrical continuity from the wall of bore 2 through float 5 to conductor 8 when the float 5 is in position to contact conductor 8. The end wall 3 is preferably a nonconductor material such as plastic, and has an insulated conductor 3,476,899 Patented Nov. 4, 1969 molded in position. End Wall 3 is further provided with an unrestricted orifice 9 to provide communication of pressures to chamber 6. End cap 4 is preferably formed of a. transparent materal, such as, clear plastic, and is provided 'with orifice 10, to communicate pressures to chamber 7. The conductor 8 is provided with a pointed contacting surface so that maiximum pressure is exerted on conductor 8 by float 5 when in engagement therewith. This pointed contact surface assures electrical continuity through conductor 8 and float 5 with a minimum amount of working pressures and electrical voltages. Electrical contacts require a predetermined pressure on the areas making contact to assure high conductivity, therefore the areas of float 5 and contact 8 that actually contact each other have a direct bearing on the sensitivity of the disclosed pressure sensing device.

It is obvious that the float 5 may be used with pressures to make or break contact with conductor 8 for the desired open or closed circuit by directing flow of pressures to move float 5 toward or away from conductor 8. F oat 5 is visable when it is against end cap 4. This provides a desirable means for observing the position of the float 5. Also the forces of gravity may be used in conjunction with the pressures to obtain the desired open or closed circuits. An adhesive strip 12 provides for easy installation of the discolsed device in its proper position. Housing 1 has a suitable terminal 15 to connect a conductor wire and conductor 8 has a terminal 16 to connect conductor wire. The light 13, battery 14 and grounds 17 show an example of an electrical circuit for the pressure sensing device.

I claim:

1. A fluid presseure sensing device comprising a housing formed of electrically conductive material having end walls defining a chamber, a lightweight fluid responsive member having substantially the same cross-sectional area as that of said chamber slidably engaging the interior surface of said chamber, said fluid responsive member consisting of a homogeneous body of carbon, electrical conductive means extending into said chamber through at least one of said end walls and being provided with a pointed contact at its inner end, said conductive means being insulated from said housing and having a terminal at its outer end. one of said end walls being provided with an outlet means and the other end wall with an inlet means, whereby fluid pressure is exerted on said fluid responsive means to move it along said chamber in response to variation of said pressure in said chamber and said fluid responsive means being adapted to engage said point contact to complete a circuit through said point, said fluid responsive member and said conductive housing.

2. A fluid pressure sensing device as set forth in claim 1 in which one of said end walls is transparent providing for visual observation of said fluid responsive member.

3. A fluid pressure sensing deivce as set forth in claim 2 in which said one transparent end wall is a cap.

4. A fluid pressure sensing device as set forth in claim 3 in which said other end wall is made of insulating material and through which said conductive .means extends.

5. A fluid pressure sensing device as set forth in claim 1 wherein said inlet means is adapted to be in communication with the Working pressures of a crankcase ventilating system 6. A fluid pressure sensing device as set forth in claim 1 wherein said inlet means is adapted to be in communication -with atmospheric pressures and said outlet means 3 4 is adapted to be in communication with the Working of 1,659,890 2/1928 Nelson 200-84 a plenum chamber of a carburetor air filter. 3,231,698 1/ 1968 Murphey et a1. 200-84 References Cited FOREIGN TE 1,501,330 7/1924 Glldge et BERNA'RD A. GILHEANY, Primary Examiner 2,446,740 8/1948 Burns 200-81 X 1,642,434 9/1927 Faun ce 200 s4 R COHRS AssistantEXaminer 

